The present invention relates to an automotive brake system with anti-locking and/or traction slip control. In this system, the wheel brakes of the regulated wheels are in communication with a brake pressure generator through pressure fluid paths. These paths are provided with electrically controllable multi-way valves open in one switch position (preferably in their rest position) and switchable to close and block the pressure fluid passage. A controllable auxiliary pressure supply system and a pressure reservoir are connected to the brake pressure generator and electronic circuits are provided for processing electric signals representing the wheel rotational behavior to generate electric brake pressure control signals to be supplied to the multi-way valves and to the auxiliary pressure supply system.
A variety of brake systems of the afore-described type are already known in the art. For example, German publication DE-OS No. 36 01 914 describes a brake system with anti-locking control, the auxiliary pressure supply system of which comprises a hydraulic pump and regulating valves limiting the auxiliary pressure to a value in proportion to the brake pedal force. Central valves in the interior of the master cylinder of this system open and close a pressure fluid conduit leading from the working chamber or chambers of the master cylinder to a pressure reservoir to regulate the auxiliary pressure. Upon commencement of the anti-locking control, the hydraulic pump is actuated thereby feeding pressure fluid to the working chambers of the master cylinder to reposition the master cylinder pistons. In the end or initial position of the pistons, the regulating central valves are opened to an extent such that a pressure proportional to the pedal force is maintained in the working chambers even though during the pressure control, pressure fluid is discharged through the output valves, from the wheel brakes into the pressure reservoir. A disadvantage with this system is that there is a substantial influence on the pistons in the master cylinder when the hydraulic pump is turned on. This influence results in a near immediate, abrupt complete restoring of the brake pedal which is objectionable to the driver.
Also, it is known to adjust the auxiliary pressure in brake systems with the aid of a regulating valve disposed externally of the master cylinder to a value proportional to the pedal force. By using separating valves to interrupt, in case of control, the connection leading from the auxiliary pressure source and the wheel brakes to the master cylinder any effect on the master cylinder and, hence, on the brake pedal, can be precluded. Additionally, separating valves of this type when used in a traction slip control system in which the working chambers of the master cylinder are in communication with the pressure reservoir, prevent pressure fluid from being discharged through the master cylinder (see, e.g., German Patent Application Nos. P 36 24 722.7; P 36 24 344.2; P 36 27 566.2). In all cases, to achieve brake pressure decrease during a skid control phase, pressure fluid is discharged with the aid of a separate outlet valve from the wheel brake of the wheel concerned to the pressure reservoir of the brake system while the pressure fluid conduit from the pressure source to the wheel brake is blocked. The control of the auxiliary pressure is thereby not influenced.
Also, it is known in the art in connection with a brake system disclosed in No. P 37 05 311.6 to have the auxiliary pressure, through regulating valves, the control input of which is in communication with the working chambers in the master cylinder, controllable in proportion to the pedal force, and to provide separating valves in the pressure fluid conduit leading from the auxiliary pressure source to the master cylinder, to directly connect a wheel brake to the pump outlet. In addition, that system provides for a bypass conduit in which a multi-way valve is located and through which the pump output can be connected to the pressure reservoir. Since regulation of the auxiliary pressure takes place externally of the master cylinder and since the hydraulic connection to the master cylinder during skid control can be isolated there are no undesirable effects on the brake pedal.